Vibronic model of laser cooling with stimulated Raman adiabatic passage pumping for Yb3+-ion-doped crystals

摘要

A vibronic model of laser cooling for crystals doped with Yb3+ ions is proposed. The model involves the stimulated Raman adiabatic passage pumping through dipole-allowed 4f-5d transitions, electron transitions between Stark-split sublevels due to vibronic interaction, and anti-Stokes fluorescence from the excited ion state. Dynamics of the cooling process are described by the density matrix formalism. It is shown that the cooling power in the case of vibronic interaction is higher at least by a factor of 3.4 compared to the case of electron-phonon interaction. In the proposed model, an increase in the cooling power yields deeper and faster refrigeration of a crystal doped with Yb3+ ions. Estimations show that, on cooling by the stimulated Raman adiabatic passage pumping, the temperature of a crystal with an irradiated volume of 2.12 x 10(-4) cm(3) can reach 64 K in a time of 2 s. In the proposed model, the cooling temperature is 30 K lower and the cooling process is 100 times faster compared to the traditional model of direct pumping. The estimates are applicable to present-day materials of technologically attainable purity. (C) 2016 Optical Society of America